I am non resident alien working in US on OPT F1 visa (exempted from SSN and Medicare), married to US citizen, should I file tax return Jointly or separate?

[jtax]

You should compute your taxes both ways and file whichever way results in less tax. Filing jointly is usually better for the taxpayers, but not always.

A possible complication is that you file jointly (have to make an election) the US will tax your world-wide income not just your US income. If you don't have a lot of foreign income that won't matter. 

For more info see:

https://www.irs.gov/individuals/international-taxpayers/nonresident-alien-spouse